The present invention relates to communications equipment. More particularly, the present invention relates to a printed circuit board which provides isolation in excess of 25 decibels (dB) in the 1 GHz range.
The ability to electrically isolate two circuits from each other is important. A first circuit is said to be isolated from a second circuit if the presence of the second circuit does not effect the output of the first circuit. Isolation is particularly important in the cable television industry where subscriptions to cable television are constantly added and deleted.
Currently, circuits are capable of providing approximately 17 dB to 20 dB of isolation at 1 GHz. At lower frequencies (e.g., less than 600 MHz) current circuits are capable of providing more than 25 dB of isolation. These current circuits typically use printed circuit boards having etched leads to aid in the amount of isolation. The present invention not only provides 25 dB of isolation in the lower frequency ranges, but also provides at least 25 dB of isolation in the 1 GHz range. The present invention attains improved electrical isolation in the 1 GHz range by using printed circuit boards having both etched leads and printed networks.
As a practical matter, improved isolation means better television reception for cable television subscribers. For instance, assume two neighbors subscribe to cable television and both televisions are connected to the same splitter. Further assume that the frequencies of operation are in the 1 GHz range and that one neighbor decides to cancel his/her cable television subscription. Once the subscription is cancelled, the one neighbor's television no longer acts as a node which serves to terminate the cable television signal. Thus, the signal can reflect onto the other neighbor's television set (with a slight time variation) causing "ghosting." Accordingly, a primary object of the invention is to provide a printed network which provides at least 25 dB of isolation in the 1 GHz range, which is unattainable by present isolation circuits.
Further objects and advantages of the present invention will become apparent in the following description.